Properties of blood vessels - L8 Flashcards
SEE slide 2 - Vascular organisation and specialisation
Blood vessels:
Arteries, arterioles, capillaries, veules, veins
What are arteries?
They are relatively large, branching vessels that
conduct blood away from the heart. Major artery is aorta
What is blood flowing in?
Blood flows in series
What are arterioles?
small branching vessels with high resistance
What are capillaries?
site of exchange between blood and tissues
Where they are offloading gases and nutrients and picking back up wastes and metabolites
What are venules?
They are small converging vessels - drain blood to veins
What are veins?
They are relatively large converging vessels that conduct blood to the heart. Major vein is vena
cava (superior and inferior)
Circulatory blood volume % ?
Systemic arterioles
Systemic capillaries
Systemic Veins
Systemic arteries
Pulmonary vessels
Heart
Systemic arterioles - 2%
Systemic capillaries - 5%
Systemic Veins - 64%
Systemic arteries - 13%
Pulmonary vessels - 9%
Heart - 7%
Special features of the artery in terms of vessel composition:
Muscular, highly elastic
Special features of the arteriole in terms of vessel composition:
Muscular, well innervated
Special features of the capillary in terms of vessel composition:
Thin walled, highly permeable
Special features of the venule in terms of vessel composition:
Thin-walled, some smooth muscle
Special features of the vein in terms of vessel composition:
Thin-walled (compared to arteries), fairly muscular, highly distensible
Another name for systemic veins?
Capacitance veins
Function of arteries:
Passageway from heart to organs which serves as pressure reservoir
Why do the arteries have to be highly elastic and highly muscular?
Highly elastic because it has to be able to stretch to accept influx coming from heart and highly muscular to be able to contract to propel blood along the way
Function of arterioles:
Primary resistance vessels that determine the distribution of cardiac output
Arterioles are well innervated by what control?
Well innervated under sympathetic control at all times, vascular tone.
Capillary - most important feature functionally and structurally and why?
1 Cell wall thick - just made up of endothelial layer, thin walled and highly permeable to allow exchange
Function of capillaries:
Site of exchange which determines the distribution of extra cellular fluid between plasma and interstitial fluid
What is important structural feature of veins?
Highly distensible
It swells as function as capacitance vessel
It is a reservoir for blood
Q. Describe microvasculature within circulatory system
talk about structure and function of microvasculature being arterioles and capillaries
macrovasculature is the arteries and veins - larger vessels
Functions of veins:
Passageway to hear from organs thats serves as blood reservoir
What does large radius of vein allow?
Allows blood flow to continue
Is there a pressure reservoir in arteries, if so what does it do?
Yes major arteries such as aorta has pressure reservoirs which received blood at high pressure as it is coming from the heart and provides continuity of flow
Arterial Pulse wave - Systolic, diastolic, dicrotic notch?
Systolic P: on ventricular contraction
Diastolic P: on ventricular relaxation
Dicrotic notch: Rebound wave or “echo” of valve closure
What kind of vessels do arterioles have?
Do arterioles have smooth muscle?
Does it have a sympathetic input?
What control does it have for resistance?
Arterioles are resistance vessels
Has a high degree of smooth muscle
Large sympathetic input
Highly sensitive control over RESISTANCE
Blood is delivered around the body to all organs at same mean arterial pressure, what is this determined by?
Level of heart and aorta
Pre capillary sphincters -
What control do they have?
Can they close over a vessel?
What do they provide resistance over?
Local metabolic control
Can seal vessel completely
Provides effective resistance over
WHOLE CAPILLARY BED
Arterioles have vasoactivity: explain what is (1) vasoconstriction and (2) vasodilation?
(1) Vasoconstriction is an increased contraction of circular smooth muscle in the arteriolar wall, which leads to increased resistance and decreased flow through the vessel
(2) Vasodilation is decreased contraction of circular smooth muscle in the arteriolar wall, which leads to decreased resistance and increased flow through the vessel
Can pulse pressure be used as indicator of heart health?
Yes ideally we want 40mL of mercury
120/80mmHg
What are pre-capillary sphincters?
They are small bands of smooth muscle that are located at the entrance of capillaries. They are responsible for regulating blood flow to the capillary beds and controlling the distribution of blood throughout the body.
What is vasoconstriction caused by actually in the body?
Caused by increased myogenic activity, increased O2, decreased CO2 and other metabolites, increased endothelin, and increased sympathetic stimulation releasing vasopressin and angiotensin 2 during the cold
What is vasodilation caused by actually in the body?
Caused by decreased myogenic activity, decreased O2, increased CO2 and other metabolites, increased nitric oxide, and decreased sympathetic stimulation releasing histamine during the heat
What is the blood brain barrier?
It is tight junctions between endothelial cells lining cerebral blood vessels and this prevents easy passage of large macromolecules and pathogens between the circulation and the brain
Explain this metabolic control and sealing of pre-sphincter capillaries:
They play a key role in local metabolic control - whether or not organ is active and they will respond if active they will open and allow blood to open, if it not under increased work at a certain moment in time it will seal the vessel completely
Veins:
1. Radius?
2. Resistance to flow?
3. Why are they called capacitance vessels?
4. What do they rely on pressure gradient for?
5. What are they assisted by in terms of posture?
- Large radii
- Little resistance to flow.
- Enormous compliance, little elastic recoil
- Capacitance vessels to store blood
- Rely on pressure gradient to maintain flow, to assist venous return
- Assisted in upright posture by valves & skeletal muscle pump (NB in exercise)
Factors that faciliate venous
How is endothelial cell important for Nitric oxide?
Innermost lining, the endothelial cell is important for secretion nitric oxide for vasodilation
NO is a potent vasodilation
What are Arterioles always controlled by? At rest under..
Arterioles always at rest under sympathetic discharge that keeps sympathetic tone or vascular tone, to keep constant resistance
EXAM Q What are physiological mechanisms that facilitate an increase in tissue metabolic activity
SLIDE 11 IS ANSWER
Bring through step by step
We have an increase in tissue metabolic activity, we need to increase O2+nutrients to those tissues - HOW?
1st of all this tissue with increased metabolic activity will have a decrease in O2 and increase in CO2 and metabolites, this need to be counterbalanced -> we need more O2 and to get rid of excess CO2 building up - this is brought about initially arteriolar vasodilation, arterioles reduce their resistance and allow more blood flow to enter capillary, pre capillary sphincters controls how many capillaries receive blood supply - they determine which route they allow blood to take across tissue bed
If we have a relaxation of these pre capillary sphincters, then we have an increase in number of open capillaries so we have an increase in capillary blood flow, if thats the case we have an increase in delivery of O2, we have ability to remove CO2 and other metabolites more quickly. By having more of these open capillaries, how does that allow that to happen?
More open capillaries means we have an increased capillary surface area available for exchange, so there are more places around actual active organ to receive O2 and give back CO2. It decreases diffusion distance from cell to open capillary, a cell is never more than 0.1mm away from a capillary, so every cell in the body is going to be perfused to be if it needs to be, thus the more open capillaries we have it means the more reduced the diffusion distance so it can go more fluidily from pressure of high to low across pressure gradient. It increases concentration gradient for these materials so basically by opening up those capillaries it makes way to offload more O2 and nutrients and make the way back of those wastes of CO2 and metabolites into venous circulation to go back to heart so the cyclec an continue indefinitely.
All of these things coming together is what will increase exchange between blood and tissue so we to support this increased metabolic activity
Don’t have to refer to exercise but we can use it as an acute stressor to explain whats happening can also refer to brain when concentrating, digestive system after eating, the list goes on…
What can resistance of arterioles by increased or decreased by ? What are the intrinsic/extrinisc factors?
The resistance can be increased or decreased if needed by myogenic activity of smooth muscle or by changing sympathetic discharge
Intrinisc factor: myogenic activity
Extrinisc factor: Discharge from sympathetic nervous supply
What are the Starling Forces
PC?
PIF?
Pie P
Pie
PC capillary hydrostatic pressure
PIF interstitial fluid hydrostatic pressure
p plasma colloid osmotic pressure (oncotic pressure)
IF interstitial fluid colloid osmotic pressure (oncotic pressure)
Is the capillary a continuous vessel?
How are endothelial cells that make up capillary cells located?
Are they tight junctions?
What makes them porous and permeable?
Yes
They are adjacent to each other, side by side
No, they have slit like gaps to allow exchange
Having these gaps
Can plasma proteins pass capillary wall?
No, we do not want them to
Plasma proteins are too big to pass however leakage can occur and they can get in - urinary tract infection - is there protein in their urine? There should not be
What do we want to offload through capillary walls?
Lipid soluble and water soluble solutes
O2+CO2
What kind of vessels are lymph vessels?
What type of endothelium layer?
Do they have valves, if so what is function?
What do they rely on for contraction?
Do they have nodes?
Where do large vessels empty into?
Blind ending capillaries - vessels
Single layer endothelium: very thin and poroud
Valves prevent back flow
Rely on skeletal muscle
contraction
Regular lymph nodes
Large vessels empty into
subclavian vein
Endothelial cells in capillaries are widespread around the body what is the only place where does this not apply?
Blood brain barrier
Major functions of lymph vessels: 4
Tissue drainage
Return leaked plasma proteins
Absorption of digested fat
Defence
What is oedema?
Is a medical condition characterised by the accumulation of excess fluid in the body’s tissues.
Oedema is typically caused by an imbalance in the fluid exchange between the blood vessels and the surrounding tissues.
Veins rely on pressure gradient to maintain flow, do they not have pumping action from the heart?
Veins do not have pumping action from heart
Most of blood that has to return from heart comes from below the heart so big mechanisms are needed to facilitate this venous return such as valves and skeletal muscle pump
Blood that comes from above, gravity helps
Oedema is the build up of fluid in the interstitium via? 4 reasons
- Reduced plasma proteins
- Increased capillary permeability
- Increased venous pressure
- Lymph blockage
How does lymph blockage occur and cause oedema?
Damage during surgery and Parasitic infection
When causes increased venous pressure and thus oedema?
Uterine venous compression during pregnancy
Aeroplane flight (via decompression & immobility i.e. ↓muscle pump activity)
What causes increased capillary permeability and cause oedema?
Inflammation and allergic responses
EXAM Q -> Explain acute control mechanisms of venous return B.P.:
Acute are sudden onset, short term right here and now mechanisms
Chronic - long term - ROS NOT FOR THIS Q
Sympathetic vasoconstrictor activity facilitates venous return: veins and arterioles are under sympathetic discharge, slight vascular tone applied keeps the resistance increased and helps increase pressure gradient
all revolve around increasing pressure gradient as we do not have support of heart behind us
skeletal muscle pump - since veins travel through this muscle, when it contracts it increases pressure in vein which increases pressure gradient which helps to improve venous return
MAJOR FACTORS ^ Sympathetic vasoconstrictor activity and skeletal muscle pump
Respiratory pump plays a small role - due to breathing activity in chest there is lower pressure in chest veins
pressure is greater within venous area below heart compared to what is in the chest, so that respiratory pressure gradient also helps to draw blood upwards but it a small contributing factor
Cardiac suction effect plays a role as well improves pressure gradient
Pressure imparted to blood by cardiac contraction - the heart contracting itself so that 70mmHg (or 17 not sure) of pressure helps improve venous pressure but not hugely
mechanical control: venous valve that are strategically located help to prevent back flow
by improving and increasing venous return we increase EDV - Frank Starling mechanism then plays in
What causes reduced plasma proteins that can lead to oedema?
Loss in urine (kidney disease)
Reduced synthesis (liver disease)
Dietary
What are starling forces?
Pressure control
important about plasma proteins is they have this sucking, drawing in effect which os why they need to stay put within the actual vessel
Blood capillary: highest pressure at arteriolar end to vein end
Ultrafiltration (kidneys) happens whereby component of plasma with its solutes and with plasma with force of hydrostatic pressure, the plasma leaves the blood and goes into interstitial tissue fluid and stays here for a period of time and then is reabsorbed back into circulation so that blood volume is not affected and stays the same, the starling force governs that with this outward pressure greater than inward pressure otherwise we would have huge reductions in blood volume that we cannot afford
Does blood leave capillaries?
No blood stays within the capillaries, only its passengers: i.e. CO2, CO2, metabolites, wastes and nutrients move in and out
Lymphatic system a filtering system?
Yes, allows blood volume to be returned to normal after filtration and reabsorption
clears this interstitial fluid that had pathogens and helps it to return back to normal circulation
plasma proteins causes a lot of leakage as it helps leaching out that tissue fluid and
Interstitium?
Tissue spaces
